Motor vehicle instrument panel with flexible tethering hinged air bag deployment door

ABSTRACT

A molded motor vehicle instrument panel made of a thermoplastic material has an integral air bag deployment door for a passenger side air bag that is defined by a tear seam and is normally retained by an integral flexible mounting/hinge flange to a part of the vehicle structure when the seam is torn by the inflating air bag and wherein this flange then bends to allow the door to swing open to allow deployment of the air bag through an opening in the instrument panel while retaining same to the vehicle structure as the door is then free of the instrument panel. At very low temperatures, a portion of the air bag door can break away from the mounting/hinge flange because of plastic embrittlement at these low temperatures and the high bending stresses encountered at this juncture. This separation of the broken door portion from the vehicle structure is prevented by a tethering hinge that is formed of a strong flexible sheet material that spans this critical juncture between the mounting/hinge flange and door and remains flexible at these very cold temperatures to retain the broken door portion to the vehicle structure.

This a divisional of application Ser. No. 08/540,471, now U.S. Pat. No.5,685,930, filed on Oct. 10, 1995, which is a continuation-in-part ofSer. No. 08/414,387 filed Apr. 25, 1995, now U.S. Pat. No. 5,564,731issued Oct. 15, 1996.

TECHNICAL FIELD

This invention relates to motor vehicle instrument panels having anintegral air bag deployment door defined by a tear seam and moreparticularly to a tether for the air bag door when it is separated atvery low temperatures from the instrument panel and then from a flexiblehinge that is integral with the door and normally provides for openingswinging movement of the door and its retention to the vehicle structureat higher temperatures.

BACKGROUND OF THE INVENTION

Presently, most passenger-side air bag doors are formed in an air bagcover that is separate from the instrument panel because the latter ismade of a commercially available thermoplastic material particularlysuited to meeting the requirements of its application but is not wellsuited to meeting the requirements of an air bag door that is defined bya tear seam formed in the instrument panel. For example, the plasticsmaterials used to make a self-supporting instrument panel must have acertain degree of stiffness and high heat resistance to meet therequirements of its application but the materials that are currentlyavailable for such an instrument panel do not retain ductility andbecome embrittled at very low or cold temperatures which is unsuitablefor air bag deployment where the air bag door is formed integral withand defined by a tear seam formed in the instrument panel.Styrene-maleic anhydride, polypropylene, polycarbonate and polyphenyleneoxide are examples of thermoplastic materials that are suitable for theinstrument panel but do not have the required ductility or flexibilityfor such an air bag door at very low temperatures. As a result, the airbag cover or door on the passenger side is normally made separate fromthe instrument panel and of a different commercially availablethermoplastic material such as polyurethane elastomer, polyesterelastomer, and polyolefin elastomer which are suitable for suchapplication but are not suitable for the requirements of the instrumentpanel.

Costs can be reduced, quality can be improved and styling can beenhanced by molding the instrument panel and the air bag cover includingan integral air bag deployment door in one piece at the same time out ofthe same commercially available material provided, however, that thenormal material requirements for the instrument panel are not sacrificedand the safe assured operability of the integral air bag deployment dooris retained at reasonable cost, even though the plastics material maynot be well suited thereto.

SUMMARY OF THE PRESENT INVENTION

A molded instrument panel made of a commercially available thermoplasticmaterial well suited for the primary purpose of such a panel has anintegral air bag deployment door for a passenger side air bag that issafely retained to the vehicle structure in a very cost effectivemanner. The air bag door is defined by a frangible tear seam in thepanel and is normally retained by an integral flexible mounting/hingeflange to a part of the vehicle structure when the seam is torn by theinflating air bag and wherein this flange which before was integral withboth the door and the panel is then separated from the panel whileremaining integral with the door and bends to allow the door to swingopen to allow deployment of the air bag through an opening in theinstrument panel while retaining same to the vehicle structure as thedoor is then free of the instrument panel. At very low temperatures, aportion of the air bag door can break away from the mounting/hingeflange where it joins therewith because of plastic embrittlement atthese low temperatures and the high bending stresses encountered at thisjuncture. This separation of the broken door portion from the vehiclestructure is prevented by provision of a flexible tethering hinge thatis formed separately from the panel of a different material andthereafter fastened to the panel so as to span the critical juncturebetween the flange and the potential break away door portion. Thetethering hinge material is of a strong flexible material that remainsflexible or ductile to a significant degree at these very coldtemperatures.

The flexible tethering hinge is fastened along one margin on one side ofthe critical juncture zone to a portion of the mounting/hinge flangeremote from this potential fracture zone by fastening means such asrivets and is fastened along another margin on the other side of thiszone to the inner side of the potential break away door portion byfastening means such as an adhesive or heat staked bosses that can notbe observed at the outer side of the door. The tethering hinge has aportion intermediate its margins that spans the potential fracture zoneand flexes when door breakage occurs to permit the broken door portionto continue to swing outward to provide for air bag deployment whileretaining the broken door portion to the vehicle structure.

According to another embodiment of the invention, the tethering hinge isformed of a second plastics material that is relatively more flexiblethan the first plastics material of the panel at temperatures below thatwhich the first plastics material becomes unacceptably brittle andsusceptible to breakage. In this embodiment, the tethering hinge iswelded to the panel by selective application of energy.

It is therefore an object of the present invention to provide a new andimproved motor vehicle instrument panel with an integral and tetheredair bag deployment door and a method of forming such a panel.

Another object is to provide a new and improved motor vehicle instrumentpanel with an integral and tethered air bag deployment door at low costand of high quality and to meet certain styling desires.

Another object is to provide a motor vehicle instrument panel having anintegral air bag deployment door that is defined by a tear seam in thepanel and is retained to the vehicle structure by a flexible tetheringhinge in the event the door is separated at very low temperatures froman integral mounting/hinge flange that normally fastens the air bag doorto the vehicle structure.

Another object is to provide a motor vehicle instrument panel includingan air bag deployment door that is defined by a tear seam in the paneland is retained to the vehicle structure by a flexible tethering hingeformed of flexible sheet material in the event the door is separated atvery low temperatures from an integral mounting/hinge flange thatnormally fastens the air bag door to the vehicle structure.

Another object is to provide a low cost, high quality, motor vehicleinstrument panel including an integral and also flexibly tethered airbag deployment door wherein the door is defined by a tear seam in thepanel and is retained to the vehicle structure by a flexible tetheringhinge formed of flexible sheet material in the event the door isseparated at very low temperatures because of cold embrittlement andbending stresses from an integral mounting/hinge flange that normallyretains the air bag door to the vehicle structure.

These and other objects, advantages and features of the presentinvention will become more apparent from the following description andthe accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a motor vehicle instrument panelincluding integral air bag deployment door with a flexible tetheringhinge according to the present invention and as installed in a motorvehicle over an air bag system;

FIG. 2 is an enlarged view taken along the line 2--2 in FIG. 1 whenlooking in the direction of the arrows and includes a diagrammatic viewof the air bag system;

FIG. 3 is a view taken along the line 3--3 in FIG. 2 when looking in thedirection of the arrows;

FIG. 4 is a view like FIG. 3 but of a much smaller cross section area inlarger relative scale and illustrates in an exaggerated manner anadhesive used to fasten the flexible tethering hinge to the air bag doorinstead of the hot staked rivets shown in FIGS. 2 and 3;

FIG. 5 is a view like FIG. 2 but showing the air bag door opened andbroken but retained during the deployment of the air bag at a very lowtemperature;

FIG. 6 is a schematic sectional view of a motor vehicle instrument panelconstructed according to an alternative embodiment of the invention;

FIG. 7 is a schematic fragmentary cross-sectional view of the panel andtethering hinge layers held by a clamping fixture in preparation forsubsequent welding according to another embodiment of the invention;

FIG. 8 is a schematic fragmentary cross-sectional view of the panel andtethering hinge layers of FIG. 7 shown joined by a weld; and

FIG. 9 is a diagrammatic view showing the process steps for forming,joining together and installing the panel and tethering hinge layers tothe vehicle structure in position over the air bag system.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 2, there is illustrated a molded motor vehicleinstrument panel 10 as installed in a motor vehicle structure generallydesignated as 11. The instrument panel 10 has an opening 12 on thedriver side for the installation of an instrument cluster (not shown)and an air bag deployment door 14 of desired shape, in this caserectangular, on the passenger side whose entire or partial perimeter, inthis case entire, is defined by a frangible tear seam 16 molded in theinstrument panel. The tear seam 16 may be formed by a groove either inthe face of the panel as shown or by a similar groove in the back sideof the panel to hide the tear seam from view as is well known in the artor by other methods known to the art of forming an integral butfrangible tear seam. When installed on the vehicle structure 11, theinstrument panel covers an air bag system 18 that is located behind theinstrument panel directly behind the air bag door 14 and is mounted on asheet metal portion 20 of the vehicle structure. The air bag system 18is of a conventional type that includes an inflatable air bag 22, aninflator 24 and an impact sensor 26 that on vehicle impact triggersignition of the inflator to inflate the air bag for deployment into thepassenger space 28 directly in front of a passenger seated on this side.

The instrument panel 10 is an injection molded one-piece part ofgenerally uniform wall thickness and is formed of a first plasticsmaterial and preferably a suitable commercially available thermoplasticmaterial such as polypropylene, polycarbonate, and styrene maleicanhydride that provides sufficient stiffness so that the panel isself-supporting to maintain the desired shape and has sufficient heatresistance to resist deformation due to heat in its interior vehicleenvironment where it is located immediately behind the windshield (notshown). The groove forming the tear seam 16 is made deep enough inrelation to the wall thickness of the instrument panel and the strengthof the plastic material so as to sufficiently weaken the wall section atthe tear seam to the point that it is torn by the force of the inflatingair bag acting against the back side of the air bag door and creates onits separation from the instrument panel an opening 30 therein for thedeployment of the air bag as illustrated in FIG. 5 and described in moredetail later.

The instrument panel 10 is fastened to portions of the vehicle structure11 at various locations outside the area of the air bag door with onesuch location being shown in FIG. 2 wherein a sheet metal screw 32fastens the panel at a lower edge thereof beneath the air bag door to asheet metal portion 34 of the vehicle structure. And it will beunderstood that similar screws or other conventional type fasteners areused at other locations outside the area of the air bag door to securelyfasten the instrument panel in place on the vehicle structure.

The air bag door 14 in the instrument panel 10 is separately fastened tothe vehicle structure by an elongated mounting/hinge flange 36 that ismolded integral with the back side of the door and extends horizontallyalong substantially the entire length and adjacent to the upper edgethereof as seen in FIGS. 1-3. The flange 36 has a flat portion 38 thatextends transversely inwardly of the door a substantial distance andterminates in a flat, angled, horizontally extending, distal portion 40that is fastened along its length by bolts 42 to a sheet metal portion44 of the vehicle structure. The flange 36 is also formed with a uniformthickness and acts as a cantilever hinge to normally provide for outwardswinging opening movement of the door when the door is separated alongthe tear seam from the instrument panel for air bag deployment. Prior tosuch air bag door separation, the flange 36 acts to fasten theinstrument panel to the vehicle structure at the air bag door and alsoprovides support for the latter against a pushing force such as from apassenger which could otherwise push the door inward and separate thedoor from the instrument panel along the tear seam.

The flange 36 is designed to normally hinge and retain the air bag door14 to the vehicle structure during its outward opening movement when thetear seam 16 is torn by the force of the inflating air bag and as suchserves as a primary tether for the door 14 to retain connection with thevehicle structure 11. In doing so, the flange 36 is highly stressed atits juncture 46 with the back side of the door as a portion 38 of theflange bends to effect swinging movement of the door. The material ofthe panel 10 and hence the flange 36 is flexible in a limitedtemperature range encompassing normal operating temperatures for mostvehicle applications (e.g. 0° F. and above). However, at very low orcold temperatures such as -20° degrees Fahrenheit and below, the typicalcommercially available plastics material suitable for the instrumentpanel in its primary application can become brittle to the point wherethe lower and major portion 48 of the door that is forced by theinflating air bag to bend outward about the horizontally extendingjuncture 46 of the door with the flange portion 38 may fracture or breakoff at this highly stressed zone (see FIG. 5) and be flung into thepassenger compartment. This is prevented in a very cost effective mannerby the strategic addition of an elongated flexible supplementaltethering hinge 50 that is formed from a sheet of strong flexiblematerial that is efficient and relatively more flexible or ductile thanthe plastics material of the panel 10 at temperatures substantiallybelow that at which the material of the instrument panel 10 becomesbrittle so as to tether the door in the event the highly stressed zone46 fractures due to embrittlement of the panel material. Examples ofsuch material for the hinge 50 are thermoplastic materials such aspolyvinyl chloride, coated nylon and Kevlar, thermosetting materialssuch as polyurethane and polyester, metal mesh screen, and a wovenfabric of fibers formed of such plastic materials or natural fibers suchas cotton or hemp.

According to the embodiment of FIGS. 1-5, the flexible tethering hinge50 extends horizontally substantially the entire length of themounting/hinge flange 36 (see FIG. 3) and is fastened along onehorizontal margin 52 of the hinge 50 on one side of the criticaljuncture zone 46 to the flat portion 38 of the mounting/hinge flange ata location remote from this potential fracture zone by fastening meanssuch as rivets 54. The tethering hinge 50 is fastened along anotherhorizontal margin 56 parallel to the margin 52 and on the other side ofthis potential fracture zone to the inner side of the potentiallyfrangible air bag door portion 48 by fastening means that can not beobserved at the outer side of the door. For example, the latterfastening means can be hot staked bosses 58 that are provided on theinner side of the door as shown in FIGS. 2, 3 and 5 such as by beingmolded integral therewith or friction welded thereto or the hiddenfastening means may be a suitable adhesive 60 as shown in FIG. 4.Examples of suitable adhesives for this purpose are polyurethanes andpolyolefins. In the case of where rivets and bosses are used to fastenthe tethering hinge at both its margins 52 and 56 respectively and wherea woven fabric as above described is employed as the tethering hinge,both of the margins 52 and 56 preferably comprise one or more folds toprovide increased strength at their points of attachment to themounting/hinge flange 36 and the potential break away door portion 48.Where an adhesive is used to fasten the woven fabric tethering hinge tothe door, only the margin 52 is preferably provided with one or morefolds to reinforce its attachment by the rivets 54 or other suitablemechanical fasteners to the mounting/hinge flange 36.

The tethering hinge 50 has a portion 62 intermediate its margins 52 and56 that spans the potential fracture zone 46 and flexes when doorbreakage occurs as illustrated in FIG. 5 to permit the broken doorportion 48 to continue to swing outward to provide for air bagdeployment while retaining the broken door portion to the vehiclestructure. The intermediate portion 62 of the flexible tethering hinge50 is preferably provided with an outward fold 63 in its installedcondition as shown in FIG. 2 that unfolds as shown in FIG. 5 on thefracturing off of the door portion 48 from the mounting/hinge flange 36to minimize the amount of stretching that is required of the tetheringhinge between it attaching means 54 and 58 or 60 to allow deployment ofthe air bag while retaining the broken door portion to the vehiclestructure.

According to another embodiment of the invention, illustrated in FIGS.6-9, the supplemental tethering hinge 50' is molded or otherwise formedseparately from the panel 10 from a second plastics material that isdifferent from the plastics material used for the panel. Theconstruction of the panel 10, the vehicle support structure 11, and airbag system 18 may be the same as that described above for the firstembodiment of FIGS. 1-5, and hence the same reference numerals will beused for those components.

The second plastics material for the supplemental tether hinge 50' isone that exhibits relatively greater flexibility or ductility than thematerial used for the panel 10 at temperatures below that which theplastics panel material becomes unacceptably brittle. Suitable plasticsmaterials for the supplemental tethering hinge 50' include polyolefinelastomer, polyurethane elastomer, polyester elastomer, silicone orrubber modified plastic; however, the means and method by which thehinge 50' is attached to the panel is different than that describedpreviously for the first embodiment.

As illustrated diagrammatically in FIG. 9, the panel 10 and tetheringhinge 50' are formed separately from one another (e.g., molded from theaforementioned first and second plastics materials, respectively) andare subsequently brought together and joined in a subsequent weldingoperation by means of which the panel 10 and tethering hinge 50' becomepermanently fused to one another.

As shown in FIG. 6, the hinge 50' is a sheet-like member having a flangeportion 52' that overlies a surface of the flange 36 adjacent the door14 of the panel 10 and conforms generally to the size and shape of theflange 36 in its preferred construction. The hinge 50' can be formedfrom sheet stock; formed by injection molding; or formed by other wellknown molding techniques such as compression molding, vacuum molding orthe like. The hinge 50' also has an integral door portion 56' thatextends across the inner side surface -of the door 14 at least to theextent that the hinge 50 does (as seen in FIG. 2) and preferably acrossthe majority of the inner side surface so as to have the same generalsize and shape as the door 14, as illustrated in FIG. 6 to provideuniform flexure of the door 14. When installed, the door portion 56' ofthe hinge 50' is generally coextensive with the door 14 and extendsacross and covers the air bag 22, but does not extend across thepreformed tear seam 16, as can be seen in FIG. 6, in order to retain thedesigned in frangibility of the tear seam 16. As with the hinge 50 ofthe first embodiment, the tethering hinge 50' has an integralintermediate portion 62' between the hinge and door portions 52', 56',that spans or bridges the highly stressed juncture zone 46 between theflange 36 and door 14 of the panel 10 and is provided for the samereason. The fold 63 provided in the embodiment of FIG. 2 is not requiredin this embodiment because the tether is more elastic than that in thefirst embodiment.

The preferred means and method of securing the supplemental tetheringhinge 50' in position on the panel 10, according to the secondembodiment, is by welding. In which the panel 10 and tethering hinge 50'are heated sufficiently at their interface at selected locations to meltand thereby fuse the two layers together at weld joints 70, illustratedschematically in FIGS. 6 and 8. One skilled in the art of weldingplastics will appreciate that any of a number of known weldingtechniques could be employed to join the two plastic layers including,for example, welding techniques such as ultrasonic, vibration,induction, hot plate conduction, electromagnetic radiation, microwaveradiation, and radio frequency welding to name a few. The selection maydepend in part on availability of the equipment, economics, andsuitability of the materials for the process. Whatever technique isselected, it should be one that develops a sufficient fusing of thematerials strong enough to withstand the load applied to the tetheringhinge 50' upon deployment of the air bag 22 so as to maintain connectionwith both the door 14 and the flange 36.

FIG. 7 illustrates schematically the general arrangement that may beemployed for welding the hinge 50' to the panel 10. As illustrated, thetethering hinge layer 50' is positioned and held by a suitable clampingfixture 72 against the panel layer 10. The fixture 72 may be of the typehaving a fixed lower platen 74 against which the tethering hinge layer50' may be placed and an upper movable platen 76 that is movablerelative to the lower platen 74 into and out of engagement with thepanel layer 10 to clamp and release, respectively, to the door 14 of thepanel 10 and tethering hinge 50' layers. The particular configuration ofthe clamping fixture tooling 72 will depend, of course, on the contourand accessibility limitations imposed by the panel 10 and they alsodiffer depending on the welding technique employed. The clamping fixture72 may also provide access to the weld-forming tooling, shownschematically in FIG. 7 at 78 as being accessible through an opening inthe lower platen 74 of the fixture 72 and movable into and out ofengagement with the tethering hinge layer 50' to develop the weld joints70. It is contemplated that one skilled in the art of welding plasticswill appreciate that the disclosed clamping fixture and welding toolingis merely schematic to illustrate the general arrangement that may beutilized and that the particular configuration and arrangement of thetooling will be dictated, in part, on the configuration of the panel 10and the welding process utilized.

The particular pattern of weld joints 70 will vary according to therequirements of the specific application. For example, FIG. 6 shows theemployment of a plurality of discrete, spaced apart weld joints 70joining the flange portion 52' of the hinge 50 to the flange 36 of thepanel 10, and joining the door portion 56' to the door 14 of the panel10. More or less welds could be utilized. For instance, all or asubstantial portion of the contacting interface could be welded ifrequired. In any case, the application of the welding should be carriedout so as to not affect the appearance of the outer exposed, so-called"class A" surface of the panel that is seen by the occupant. In otherwords, the development of the weld joints 70 should be controlled sothat when formed, they are not visibly detectable on the class A surface(e.g., there should be no melting, depressions, or other weld-inducedimperfections on the class A surface).

By molding the tethering hinge 50' separately from the panel 10, itallows the panel 10 and tethering hinge 50' to be tested individuallyfor performance before being joined and further simplifies theapplication of the tethering hinge material 50' to the back side of thepanel 10 more particularly in applications in which the panel 10 has acomplicated contour, including undercut regions which would make itdifficult to mold the tethering hinge 50' in place against the panel 10.

The invention has been described in an illustrative manner with respectto presently preferred embodiments, and it is to be understood that theterminology that has been used is intended to be in the nature of wordsof description rather than words of limitation. Obviously, manymodifications and variations of the present invention in light of theabove teachings nay be made. It is therefore to be understood thatwithin the scope of the appended claims, the invention may be practicedotherwise than as specifically shown and described.

What is claimed is:
 1. In combination,a motor vehicle structure, an airbag system including an inflatable air bag supported on said vehiclestructure, a molded instrument panel made of plastics material mountedon said vehicle structure and covering said air bag, said instrumentpanel having one or more frangible regions, at least one of saidfrangible regions comprising a tear seam defining at least a portion ofa perimeter of an air bag deployment door in said instrument panel thatis torn outward from said instrument panel along said tear seam by theforce of said air bag on inflation to form an opening in said instrumentpanel allowing deployment of said air bag into a passenger space in saidvehicle structure, said door portion of said instrument panel subject toembrittlement at temperatures below a limited temperature range andsubject to fragmentation during air bag deployment below said limitedtemperature range, and a flexible tethering hinge formed of flexiblematerial that remains flexible at temperatures substantially below saidlimited temperature range, said tethering hinge extending substantiallya length of the door portion of said instrument panel along an innerside of a major portion of said door portion of said instrument paneland along a second portion of said instrument panel spaced from saidmajor portion of said door portion of said instrument panel saidtethering hinge having one margin that is located against and connectedto said second portion of said instrument panel and having a secondmargin that is located against and connected to said inner side of saidmajor portion of said door portion of said instrument panel withoutdisrupting an outer side of said door portion, and having anintermediate portion that is located between said margins and spans saidfrangible region disposed between said major portion of said doorportion of said instrument panel and said second portion of saidinstrument panel.
 2. The combination set forth in claim 1 wherein saidintermediate portion of said tethering hinge has a fold that extendsalong and outward of said frangible region between said major portion ofsaid instrument panel and said second portion of said instrument paneland unfolds to retain said major portion of said door portion of saidinstrument panel to said vehicle structure when said frangible regionbreaks.
 3. The combination set forth in claim 1 wherein mechanicalfasteners connect said one margin to said second portion of saidinstrument panel, and an adhesive connects said second margin to saidmajor portion of said door portion of said instrument panel.
 4. Thecombination set forth in claim 1 wherein mechanical fasteners connectsaid one margin to said second portion of said instrument panel, and hotstaked bosses on said inner side of said major door portion of saidinstrument panel connect said second margin to said major portion ofsaid door portion of said instrument panel.
 5. The combination set forthin claim 1 wherein said flexible material is a thermoplastic sheetmaterial.
 6. The combination set forth in claim 1 wherein said flexiblematerial is a metal mesh screen.
 7. The combination set forth in claim 1wherein said flexible material is a woven fabric of plastic fibers. 8.The combination set forth in claim 1 wherein said flexible material is awoven fabric of natural fibers.
 9. The combination set forth in claim 1wherein said door portion of said instrument panel includes an integralelongated mounting/hinge flange located on an inner side of said doorportion, said mounting hinge/flange comprising said second portion ofsaid instrument panel, said mounting/hinge flange being fastened to saidvehicle structure to normally aid in securing said instrument panel inplace on said vehicle structure and supporting said door portion againstan inward pushing force when said air bag is not being deployed, saidmounting/hinge flange being flexible in said limited temperature rangeto act as a hinge and swing said major portion of said door portion ofsaid instrument panel outward for air bag deployment while retainingsaid major portion of said door portion to said vehicle structure, themounting hinge/flange subject to breakage along a juncture zone withsaid major portion of said door portion of said instrument panel attemperatures below said limited temperature range whereby said majorportion of said door portion is separated from said mounting/hingeflange and thereby from said air bag system, said juncture zonecomprising said frangible region that is disposed between said majorportion of said door portion of said instrument panel and said secondportion of said instrument panel.
 10. The combination set forth in claim9 wherein said mounting/hinge flange extends substantially the length ofsaid door, and said tethering hinge extends substantially the length ofsaid mounting/hinge flange.
 11. The combination set forth in claim 9wherein said mounting/hinge flange extends substantially the length ofsaid door, said tethering hinge extends substantially the length of saidmounting/hinge flange, and said intermediate portion of said tetheringhinge includes a fold located opposite said juncture zone.
 12. Thecombination set forth in claim 1 wherein said flexible material is athermosetting material.
 13. The combination set forth in claim 1 whereinsaid second margin of said tethering hinge is connected to said innerside of said major portion of said door portion of said instrument panelby fusing.
 14. The combination set forth in claim 1 wherein:mechanicalfasteners connect said one margin to said second portion of saidinstrument panel; and an adhesive connects said second margin to saidinner side of said major portion of said door portion of said instrumentpanel.
 15. The combination set forth in claim 1 wherein:mechanicalfasteners connect said one margin to said second portion of saidinstrument panel; and fasteners including hot-staked bosses disposed onsaid inner side of said major portion of said door portion of saidinstrument panel connect said second margin to said major portion ofsaid door portion of said instrument panel.
 16. The combination setforth in claim 1 wherein said intermediate portion of said tetheringhinge spans said frangible region between said major portion of saidinstrument panel and said second portion of said instrument panelwithout said intermediate portion being connected to said frangibleregion.
 17. In combination, a motor vehicle structure, an air bag systemincluding an inflatable air bag, a molded instrument panel made ofplastics material mounted on said vehicle structure and covering saidair bag, said instrument panel having two or more frangible regions, oneof said frangible regions comprising a tear seam and one of saidfrangible regions comprising a door hinge, said tear seam and said doorhinge together defining an air bag deployment door in said instrumentpanel that is torn outward from said instrument panel along said tearseam by the force of said air bag on inflation to rotate around saiddoor hinge to form an opening in said instrument panel allowingdeployment of said air bag into a passenger space in said vehiclestructure, said door hinge subject to embrittlement at temperaturesbelow a limited temperature range and subject to breakage at thosetemperatures during air bag deployment whereby at least a portion ofsaid door portion of said instrument panel is at least partiallyseparated from said door hinge and thereby from said air bag system, anda flexible tethering hinge for said door portion formed of flexiblematerial that remains flexible at temperatures substantially below saidlimited temperature range, said tethering hinge spanning one of saidfrangible regions from an inner side of a major portion of said doorportion of said instrument panel to a second portion of said instrumentpanel, said tethering hinge having one margin that is located againstand connected to said second portion of said instrument panel at alocation spaced from said frangible region spanned by said tetheringhinge and having a second margin that is located against and connectedto an inner side of said major portion of said door portion of saidinstrument panel without disrupting an outer side of said door portionand having an intermediate portion that is located between said marginsand spans said frangible region.
 18. The combination set forth in claim17, wherein said second margin of said tethering hinge is connected tosaid inner side of said major portion of said door portion by fusing.19. The combination set forth in claim 17, wherein:mechanical fastenersconnect said one margin to said second portion of said instrument panel;and an adhesive connects said second margin to said inner side of saidmajor portion of said door portion.
 20. The combination set forth inclaim 17, wherein:mechanical fasteners connect said one margin to saidinner side of said second portion of said instrument panel; andfasteners including hot-staked bosses disposed on said inner side ofsaid major portion of said door portion connect said second margin tosaid major portion of said door portion.
 21. In combination, a motorvehicle structure, an air bag system including an inflatable air bagmounted on said vehicle structure, a molded panel made of a firstplastics material mounted on said vehicle structure and covering saidair bag, said panel having a tear seam defining an air bag deploymentdoor in said panel that is torn outward from said panel along said tearseam by the force of said air bag on inflation to form an opening insaid instrument panel allowing deployment of said air bag into apassenger space in said vehicle structure, said door having an integralelongated mounting/hinge flange located on an inner side and secured tosaid vehicle structure to normally aid in securing said panel in placeon said vehicle structure, said mounting/hinge flange being flexible ina limited temperature range to act as a hinge to swing said door outwardfor air bag deployment while acting as a primary tether to retain saiddoor to said vehicle structure but said flange being subject to breakagealong a juncture zone with said door at temperatures below said limitedtemperature range whereby a portion of said door may become separatedfrom said mounting/hinge flange and thereby from said vehicle structure,and a flexible supplemental low temperature tethering hinge for saiddoor formed separately from said panel of a second plastics flexiblematerial that is relatively more flexible than said first plasticsmaterial at temperatures below said limited temperature range, saidsupplemental tethering hinge having a flange portion positioned againstsaid mounting/hinge flange, a door portion positioned against an innerside surface of said door and an intermediate portion spanning saidjuncture zone, wherein said supplemental tethering hinge is fixed tosaid panel by weld joints.
 22. The combination set forth in claim 21wherein said panel has an outer side surface opposite said inner sidesurface, said weld joints being visually undetectable from said outerside surface.
 23. The combination set forth in claim 21 wherein saidsupplemental tethering hinge overlies said air bag.